When Ford (NYSE: F) took the wraps off its impressive new Fusion sedan on Monday, analysts and industry watchers (including this humble Fool) immediately started pondering the possibilities: Would this be the car that would finally knock Toyota's (NYSE: TM) Camry off its best-selling pedestal?

The answer to that question isn't simple. Toyota has had its troubles but retains fierce consumer loyalty, but a couple of days after the car's debut, another question struck me: Could the Fusion -- specifically, the Fusion Energi, a plug-in hybrid version that's due later this year -- be a problem for Tesla Motors (Nasdaq: TSLA)?

A potential wrench in Tesla's works?
Tesla, of course, is on track to launch its all-electric Model S sedan later in 2012 -- a launch that will be the make-or-break moment for the audacious Silicon Valley startup. That launch will almost certainly be a success, at least initially -- Tesla has thousands of preorders (and $5,000 deposits) and has already said that the initial production run is sold out -- but for Tesla to succeed as a business, the Model S has to get sustainable sales traction, to find customers beyond the circle of well-heeled gadget geeks and early adopters who ponied up all those deposits.

That's where things start to get complicated for Tesla, and that's where the Fusion Energi could represent a problem -- or at least the beginning of one -- for the upstart automaker. The Model S's value proposition is that it's new technology, it's green (you won't use any gas), it's practical, and it's in a stylish package from an exciting new company.

But what if there was an alternative that was also attractively packaged, just as practical, and nearly as green (you won't use much gas, and you might go for days without using any at all) -- but from a stable, trusted automaker that isn't some crazy startup out in California? That's the Fusion Energi -- a "plug-in" hybrid version of Ford's hot new sedan. While it'll have a gas engine along with its electric drivetrain, the "plug-in" feature means you'll be able to charge it up at home -- and drive for a while without using a drop of gas.

Oh, and it's probably going to be a lot cheaper than the Tesla, too. Ford hasn't announced specifics yet, but my semi-educated guess is that the Fusion Energi will be priced at or a bit below $40,000. Compare with the Model S, which starts at $57,400 for a stripped-down base model and goes up (sharply) from there as you add range and features.

You see where I'm going with this?

Tesla shareholders, ponder this carefully
I can hear the Tesla fans howling already, but hear me out: There's an important point here. Yes, the electric-only range of the Fusion Energy is likely to be something like 40 miles, versus the 160 miles you'll get in that entry-level Model S, but how long is the average daily commute? And while greentech purists will scoff at the idea of buying a car that uses any gas, those aren't the people Tesla needs to win over.

The purists, at least the ones who can afford it, have already put money down for a Model S. It's the people who are intrigued but skeptical, who are today driving a comparably priced car like a BMW or a Lexus, that Tesla needs to win over to get to sustainable profitability.

Now, maybe those people won't be interested in a pedestrian Ford, even one that (like the Model S) comes with a high-tech aura and borrows more than a bit of its styling from sleek Aston Martin coupes. But here's the thing I want you to take away: There are going to be a lot more cars like the Fusion Energi making their debuts in the months to come -- and some of them will be smack in the Model S's price range.

The competition is coming, and it's coming soon
Nissan already has the all-electric Leaf and is working on an all-electric luxury car for its premium Infiniti brand that will arrive next year. General Motors (NYSE: GM) has already announced a Cadillac that will use the Chevy Volt's plug-in technology. Toyota just launched a plug-in Prius and has other advanced hybrid and electric drivetrains under development, some of which will end up in upscale Lexus models (which already has several hybrids available).

And it's a safe bet that Honda (NYSE: HMC), which is beginning the same kind of product-line overhaul that Ford went through a few years back, will have some significant green vehicles to announce in the coming months -- as will Ford's own upscale Lincoln brand, which will emphasize advanced green technology in all of its new models.

It's true that none of these will offer quite the same kind of cachet that Tesla has worked hard to cultivate for the Model S. And it's possible that none of them will be able to match the 300-mile electric-only range of a fully loaded Model S, at least not right away. Those two factors alone will win Tesla some sales, no matter what else comes along. But on the other hand, all of them will offer something Tesla can't -- the peace of mind and wide support network one gets when buying from a long-established automaker. And in the case of the hybrids, the peace of mind of having a tried-and-true technology -- that gas engine -- to fall back on.

How much of a difference will that make? We'll find out. But Tesla shareholders who don't take these competitive threats seriously may be in for a rude surprise.

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